V20W Datasheet, PDF (14/24 Pages) List of Unclassifed Manufacturers – PIEZOELECTRIC ENERGY HARVESTERS

APPLICATIONS INFORMATION - SWITCHED CAPACITOR BOOST CIRCUIT
Switched Capacitor Boost Circuit for One-
Shot Sensors and Low Vibration Levels
It is often difficult to make use of low-voltage energy
scavenging sources, such as piezo energy harvesters
at low vibration amplitudes, solar cells in overcast or
indoor environments, or Seebeck devices, etc., as
most microcontrollers and sensors require minimum
voltages of 1.8V or greater to operate. Using these
sources requires a voltage boost converter with a
minimum start-up voltage, low start-up current
requirement, and graceful handling of undervoltage and
slow input voltage rise times.
The circuit shown, based on the Seiko Epson S-882Z
series charge pump IC, provides bursts of power
starting at approximately 2.4VDC (ending at 1.6-2
VDC) from input voltages as low as approximately
380mV. This IC provides boosting using small on-chip
switched (“flying”) capacitors, rather than inductive
boost conversion. Thus the initial input current
requirements are reduced compared to a typical boost
conver ter, requiring only a small power-supply
bypass capacitance to reliably start up. The circuit
can begin operating almost immediately when power
becomes available. This circuit is ideal for directly
powering small sensors that can perform their
function (e.g. record or transmit a measurement) in a
known amount of time and power. It could also be
used to extend battery life, or as a trigger source for
devices with their own battery/supercap power
source.
When the voltage at VIN exceeds the minimum start-up
voltage, the IC begins pumping charge to a storage
capacitor connected across the CPOUT pin. When the
capacitor voltage reaches 2.4V, the output is enabled
and this voltage is applied to the load. The load is
automatically disconnected when the storage capacitor
voltage drops below approx. 1.8V (see Figure 6). This
behavior allows the circuit to directly power most 3.3V
microcontroller circuits, with a typical operating voltage
range of 1.8V ~ 3.6V, without exposing the circuit to
significant undervoltage or unfavorable voltage rise-
time conditions.
Piezo Bimorph
J3
X1
S-882Z
VH
3
4
VM
VIN
2
5
GND
D1
CPOUT
1
VOUT
VCC
BAT54STA
C1
U1
X2
1
QPXX_RA
10uF
D2
GND
C3
100uF
GND
GND
REVISION N0. 002 REVISION DATE: 01-23-2013
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